1. Field of the Invention.
The present invention relates to a modular transmitter construction wherein transmitter body components can be easily assembled into a complete transmitter for permitting forming a wide number of different transmitters utilizing a relatively low number of individual components.
2. Description of the Prior Art.
Differential pressure transducers which have a deflecting sensing diaphragm coupled to isolation diaphragms are commonly known. The isolation diaphragms are slack diaphragms that isolate the sensing diaphragm from the corrosive process fluid being sensed. In order to transfer pressures from the isolation diaphragms to the sensing modules, a substantially noncompressible fluid fill is provided in passageways and chambers between the isolation diaphragms and the sensing diaphragms. It has been a common practice to assemble sensor and isolation diaphragm components in a subassembly and then the passageways and chambers are filled with the noncompressible fluid. Usually a separate fill tube leading to the chambers and passageways is provided for filling and the fill tube sealed off when the filling is accomplished. The filling itself generally requires submerging the subassembly during the filling process and then pinching off the fill tubes. The subassemblies thus take a long time to build and have a high labor and material cost.
When such subassembly including the sensor and isolation modules was made, the failure of any of the parts, such as the sensing diaphragm or an isolation diaphragm during the manufacturing process would result in scrapping the entire costly subassembly. It also was necessary to stock virtually all of the available options as finished subassemblies, in order to meet reasonable delivery schedules, thereby increasing substantially the capital required for inventory.
FIG. 1 of the drawings in this application schematically shows a typical prior art arrangement, including a transmitter 10 that has a sensor body 15, and an isolation body 12. The isolation body 12 includes isolation diaphragms 13 and 14, that enclose chambers 13A and 14A that are filled with a substantially noncompressible fluid. In order to connect these chambers 13A and 14A to a sensor body 15, tubes 16 and 17 respectively are connected to passageways in the isolation body 12 and welded in place with suitable welds indicated at 16A and 17A respectively. The tubes open to chambers on opposite sides of a sensing diaphragm 15A. In order to fill the tubes 16, 17 as well as the chambers on opposite sides of the sensing diaphragm 15A for the sensor 15, fill tubes indicated generally at 18 and 19 are provided in the isolation body and extend from the exterior thereof into the chambers 13A and 14A, respectively. The chambers, tubes and passageways may be evacuated and silicone oil is then filled in through these fill tubes. The fill tubes are pinched off and sealed by welding or with suitable caps. In order to make the assembly, it requires substantial labor, and the subassemblies of the sensor body and the isolator body become quite expensive. For each different transmitter configuration (i.e. different pressure range or the like), each individual configuration has to be separately made as a complete subassembly.